I have a C. Stiegele hammer drilling I acquired a few years ago on which the left hammer would not hold back. Upon disassembling it, I found that the screw holding one of the springs underneath the mainspring had snapped off in the hole. The majority of the threaded portion is stuck in the lockplate hole. Picture is below.



I seriously considered trying to sell this as a fixer upper and may still do so, but I thought I would give it one last chance. Any advice on how to get this stuck portion out?

From the broken off remnant I was able to determine that the threading seems to be M2x0.4, and I picked up two screws from the local hardware store. My plan was to remove the broken piece from the sidelock plate, install a new screw all the way through, then cut off the end sticking out. Originality is not a concern, as this is a well-used drilling with one buttstock screw already replaced with a nail. Just trying to get this functional enough to shoot.

But my conundrum is trying to get this screw out. I have a 1/32" end mill, but it looks so fragile that I doubt I could use it to remove the stuck end. Should I use a larger drill bit? Try to slot the end for a flat head jewelers screwdriver? I'm open to suggestions.

I would clamp it to a piece of flat stock, put the stock in a vise, center drill the old screw are carefully drill out the old screw. It is a through hole and should be pretty easy to do. I have done lots of them this way, much harder in a blind hole.

pomofo,
Since you have the lock out, I suggest you take it apart, buy a lefthand drill of appropriate size and drill it out, after soaking with penetrating oil. If you are lucky, the lefthand drill will unscrew it. You mentioned having an end mill, so I'm guessing you have a milling machine that will turn in reverse.
Mike

Do you have the sear spring?

To further refine the two suggestions made above, you could also buy a left hand center drill, which would make this task easier, and reduce the possibility of the drill bit walking off the center of a 2 m/m screw. W.W. Grainger and MSC sell left hand center drills, and the #1 size would have drill tips that are 1.1906 m/m dia.

https://www.grainger.com/category/machining/drilling-and-holemaking/countersinks-center-drills-spotting-drills/center-drills?attrs=Cutting+Direction+-+Machining%7CLeft+Hand&filters=attrs

https://www.mscdirect.com/product/details/01043017

I also agree with the idea to soak it with a good penetrating oil, and give that several days to get into those tiny threads. I'd dip into my emergency stock of the now discontinued Tasgon for a job like this, but I have found that pure oil of wintergreen is very good on small fasteners as a penetrating oil. About a week ago, I was able to remove the remnants of four 3 m/m screws that sheared off flush with the surface. But they weren't rusted, and I was able to catch the edge with a dental pick, and turn them out far enough to grab a thread with small needle nose pliers to remove them. You may want to try that first, using a very small pointed punch near the edge to get things started counterclockwise. I find I am able to remove a good percentage of broken screws without resorting to drilling.

I find it very surprising that your broken screw seems to be a standard metric thread, and not some obscure bastard size. Good luck.

Broken pins in blind holes I must admit are one problem that can reduce to putting the whole shooting match in the trash. Though I do succeed in removing the broken piece more often than not.
I would strip the lock then use the two things that have a good track record of working in this situation, heat and cold. Because of the movement caused by heat and cold sometimes the the screw stub can become loose and turned out if there is enough to get hold of. I use Electronic freezer spray and a small flame butane torch a number of times in succession then add a couple of drops of penetrating oil then heat gently, this helps the oil to creep down the threads. I then work on the side of the broken stub with an old jewelers screwdriver freshly ground to be sharp, tap with a light hammer so it cuts in then using gentle taps towards the left seeing if It is possible to turn the screw. Another approach is to try to cut a slot in the top of the broken screw to take a screwdriver. As to the thread you say M2 it could also be BA 9 is 1.9mm and 8 is 2.2mm.

I like the lefthand center drill idea.
Mike

I think I'll try the left hand center drill, using penetrating oil in the meantime to make sure the screw loosens. Hopefully I can get something in before Christmas. The dental pick method sounds interesting too, thankfully I just ran across one last week as I was organizing my tool drawer, didn't even realize I had one. Many thanks to everyone for all the good advice.

pomofo, if like you said the screw hole goes through the lock plate I would would use a drill smaller than the screw and have than area elevated, use some penetrating oil and the force of the drill on the broken screw should run it out of the other side.
A blind hole can be a lot more challenging.

Just a thought, if the screw is not rust seized, maybe a neodymium magnet could make it turn without drills etc. Like I said, just a thought.

BA (British Association) would, I think never be used for drillings which were never made in Britain to my knowledge.
I would go for it being a metric thread.
If it could be centered up in a milling machine then a 1.8mm shank brought down at say 500 rpm with some pressure and turning counterclockwise it might weld itself onto the broken shank and unscrew.